A poorly formed fuel/air intake charge, including inadequately atomized or vaporized fuel, and the resultant presence of raw fuel in the intake tract extending from the intake charge forming device to the combustion chamber, as well as back pressure and its resultant reversion, explained more fully below, are well known conditions that adversely affect induction and combustion in virtually every type of internal combustion engine utilizing virtually all known kinds of charge forming or fuel/air mixing devices, including carburetors, fuel injectors, and hybrids of the two. Such conditions occur under even ideal operating conditions, with a poorly or inadequately formed intake charge and raw or liquid fuel in the intake tract being particularly problematic during cold starts, rapid or sudden throttle changes and the like. Poor charge formation is aggravated by malfunctioning, dirty, or improperly set-up or adjusted charge forming devices, as well as other problems such as vacuum leaks and faulty emissions control devices. The resultant raw fuel tends to collect in low spots in the intake tract where it can evaporate, but can also travel on to the combustion chamber. An inadequately atomized or vaporized fuel charge, along with raw fuel that reaches the combustion chamber, can cause poor combustion, engine response, power, and economy, as well as spark plug and valve fouling, dirty exhaust emissions and other problems. Back pressure and reversion primarily disrupt induction, which is the aspiration of the intake charge into and through the intake tract, and therefore the delivery of the propel mix of fuel and air to the combustion chamber responsive to changes in throttle and power demand.
Numerous devices have been utilized over the years to address mostly individually the problems of improper intake charge atomization and/or vaporization, raw fuel in the intake tract, and back pressure and/or reversion. Reference for instance, U.S. Pat. No. 4,381,756, which discloses a gasoline economizing attachment device that can be mounted between a carburetor and intake manifold of an internal combustion engine to vaporize uncarbureted fuel in the intake tract. This device includes an annular upstream facing chamber or recess for collecting uncarbureted fuel at the exit port of the carburetor, and an external vaporizing system which utilizes the pressure differential between the intake manifold vacuum and an outside source of air, presumably the atmosphere, to vaporize the collected fuel and return it to the manifold. Shortcomings of this construction, however, include that it does not significantly improve overall intake charge vaporization, nor does it address the problem of back pressure and reversion and their effects on induction. Also, the device restricts air flow through the intake tract to at least some degree, it is relatively complex, and requires an outside air source to effect vaporization of the fuel.
Other examples of known devices for improving fuel atomization and vaporization are disclosed in U.S. Pat. Nos. 4,295,458; 4,452,219; 4,974,573; 3,747,581; and 4,672,940. Each of these devices utilize some type of perforated structure, such as a mesh or a screen member, through which the intake charge is directed to improve fuel atomization, the latter two devices utilizing heat to vaporize the fuel. Shortcomings of all of these devices include the flow restrictiveness of the screen or other perforated member, and with regard to the latter two devices, the requirement of heat to vaporize the fuel. Vaporizing the fuel using heat is considered a shortcoming because a heated fuel charge has been found to be less dense and thus less powerful when combusted, and makes it more difficult to achieve higher levels of volumetric efficiency. The means required to heat the fuel also adds complexity and expense. Further, if too hot, fuel vapor in the intake tract can lead to the condition commonly known as vapor lock which is a condition that partially or completely blocks the flow of fuel into the intake charge path. To avoid vapor lock, some of the prior devices heat the fuel only during engine warm-up and are turned off when the engine reaches its operating temperature. However, an obvious shortcoming With those devices is that they provide less benefit when unheated. These constructions also do nothing to significantly address back pressure and reversion.
Reference U.S. Pat. Nos. 3,458,297; 3,847,125; 4,058,102; and 5,392,752, which disclose various known devices for removing raw fuel from the intake passages of internal combustion engines. Each of these devices utilize some type of cup or other member to collect the liquid fuel as it travels through the intake passage, and means to mix the collected fuel into the intake charge so that the fuel can be carried by the charge flow to the combustion chamber. Reference in particular U.S. Pat. No. 3,458,297, which discloses several embodiments of a ring shaped body member that mounts in an intake passage and forms an annular recess therearound for collecting fuel along the intake passage wall. A plurality of projections are located at spaced intervals around the central opening through the member, and a plurality of radial passageways extend through the member to carry the collected fuel from the annular recess to the projections. Each projection includes a chisel shaped drip edge for receiving the fuel such that the intake charge can flow over the drip edges, pick up the fuel, and carry it to the combustion chamber. U.S. Pat. No. 3,458,297 also discloses one embodiment that utilizes exhaust heat of the engine to vaporize the fuel to facilitate pick up by the intake flow. However, neither this or the other identified devices effect improved overall intake charge vaporization or address the problem of back pressure and reversion, and all restrict intake flow at least to some extent.
Reversion, as noted above, is the result of back pressure and can be more particularly described as the reverse or back flow of a portion of the intake charge through an intake tract of an engine as a result of a pattern or series of reverse or upstream traveling shock waves or pulses that enter the intake tract when the intake valve or other means controlling the flow of the intake charge into the combustion chamber is open. These shock waves or pulses are the result of the high pressure developed by combustion in the combustion chamber, and also back pressure from the exhaust, both of which can be transmitted to the intake tract through the open intake valve to contaminate the intake charge. Such upstream or back flowing pulses and back pressure have been observed to move mainly through the stagnant or dead spaces in the intake tract where the intake flow has little or no velocity, and more importantly, along the wall of the intake tract in essentially the boundary layer of the intake charge flow stream. The upstream traveling pulses and back pressure cause some of the adjacent downstream traveling intake charge flow to be slowed, stalled, or even reversed, the latter instance constituting reversion. The upstream traveling pulses and back pressure tend to decrease or dilute intake vacuum signal somewhat, which is a measure in terms of negative pressure or partial vacuum of the suction at a particular location in the intake tract from the intake stroke of the engine. A decreased vacuum signal represents a corresponding drop in induction as well as a resultant loss in engine responsiveness and smoothness.
Reversion and back pressure, sometimes referred to hereinafter as just reversion, are usually more problematic in two stroke internal combustion engines of all types, including those utilizing piston porting, conventional valves, reed valves, and also rotary valves for controlling communication between the intake tract and combustion chamber. This is for several reasons, namely, because two stroke engines operate at higher speeds than four stroke engines, and because two stroke engines lack a separate intake stroke compared to four stroke engines, the intake valve is open more frequently than in a four stroke engine. Reversion is also a problem in both two and four stroke engines having a substantial valve overlap condition, that is, wherein the intake valve is open simultaneously with the exhaust valve, and in virtually any engine when operating under heavy load conditions such as while powering a vehicle in a climb. Reversion has been found to be so great in some engines, particularly two stroke engines, that the engines won't operate without means to reduce or contain the reversion. Known constructions effective for reducing or containing reversion include devices known as reversion traps, usually located in the intake passage, and reversion tubes, usually located in the exhaust passage. Reversion traps generally include a restriction or neck in the exhaust passage upstream of a larger expansion area or chamber, which restriction or neck traps or limits the back flow of pressure and contaminants through the conduit. Reversion tubes operate generally the same as reversion traps, but in the intake passage. Shortcomings of both devices include that they do little or nothing to improve intake charge atomization and/or vaporization and do not recapture any of the energy of the reverse pulses or back pressure. Reversion traps are also limited in that although they reduce back pressure generated in the exhaust, they do no limit that emanating from the combustion chamber. A further problem with reversion is that it can be hot, due to its origin in the combustion chamber and exhaust, and although hot reversion can facilitate vaporization of the fuel charge, it is a shortcoming for the reasons noted above with respect to hot fuel vapor.
Other known apparatus pertinent to a discussion regarding induction include the exhaust driven device called a turbocharger. A turbocharger generally comprises a pair of turbines mounted to a common shaft. One turbine is a drive turbine disposed in the exhaust flow path of an engine, while the other turbine is a compressor turbine disposed in the intake flow path between the charge forming or fuel/air mixing device and the combustion chamber. In operation, the exhaust gases expand across the exhaust turbine to rotate it and the intake turbine thereby compressing the intake charge and forcing induction. This compression permits an increase in the amount of the fuel introduced into each combustion chamber during the intake stroke, while maintaining a desired fuel/air ratio, to produce attendant increases in engine power output and volumetric efficiency. However, shortcomings associated with turbochargers include the heating of the intake charge due to compression thereof, which is a problem often remedied utilizing a device commonly called an intercooler. The purpose of an intercooler is to remove the heat generated as the intake charge is compressed so that the fuel mixture density is increased. However, shortcomings of intercooled turbochargers include added weight, complexity, and expense. Also, since turbochargers are driven by exhaust gases, when exhaust gas flow is low, such as when an engine is idling or under only light load, the turbocharger generally does not operate to compress the intake charge or facilitate induction. Turbochargers furthermore have slow response to demands for power increase and will consume excess fuel for a time whenever there is a significant increase in throttle opening. Still further, due to the location of the turbocharger drive turbine in the hot exhaust flow, turbochargers have been found more prone to heat related failures.